1. Field of the Invention
The present invention generally relates to a method for reserving a new CoA (New Care-of Address, hereinafter, to be referred to as “NCoA”) to achieve a fast hand-off under a mobile IPv6 (Internet Protocol version 6) environment, and more particularly, a method for reserving a new CoA in advance to reduce the time necessary for generating a CoA and performing a fast hand-off by using the new CoA reserved in advance in another network before a mobile node linked to a foreign network is moved to another network.
2. Description of the Related Art
Recently, with the rapidly increasing use of the Internet, the development of radio communications technology, and the improvement of performance of mobile terminals such as a portable computer, PDA (Personal Digital Assistant), users using wireless Internet have increased. Under a wireless Internet environment, the mobile terminal occasionally changes its network connection site with the movement of its location occasionally. Such a mobile terminal is referred to as a mobile node.
In order for the mobile node to perform wireless Internet communication, even when the mobile node moves to a foreign network out of its home network, it is necessary that a high quality Internet service identical to that of the home network is assured. Even when the mobile node changes its network connection site, a variety of technologies have been proposed to provide a stable wireless Internet service. Of special note, the Internet Engineering Task Force (IETF), which is a mobile IP working group, has proposed a method by which all mobile terminals can continuously use a specific identifier, referred to as an IP address, regardless of the network connection site. This method defines a mobile IP protocol and complements defects, and allows tasks to be continued to be performed when the mobile device changes networks. Also, in order to overcome a problem that the existing IPv4 address system is not able to accept increasing address demands, the introduction of mobile IPv6 technology is underway to provide wireless internet service using the IPv6.
In accordance with the mobile IPv6 technology, even when a mobile node moves to a foreign network, the mobile node communicates with a correspondent node (CN) using its home address (HA) via a home agent (HA) which is a router having its registration information. When the mobile node is linked to the foreign network, the mobile node is assigned with a CoA (care of Address), which is a temporal address from an access router of the foreign network, and registers the assigned CoA along with the home address at the home agent, which is called a binding.
Accordingly, the home agent intercepts packets from the correspondent node to the mobile node, and forewords the packets to a mobile node located at the foreign network using a current CoA of the mobile node.
In order to be assigned a CoA, the mobile node makes a link layer connection to the foreign network, and then receives a router advertisement (RA) message from a router of the foreign network. To this end, the mobile node may multicast a router solicitation message to the overall network.
The router advertisement message provides prefix information of the network. Accordingly, the mobile node generates a new CoA using the prefix information of the network and its link layer address (LLA). The mobile node sets the generated CoA as a temporal address.
When it is not possible to determine if the CoA is generated according to the movement of the mobile node to the network or the re-setting-of the network interface of the mobile node, delay should be carried out for a time between 0 and 1 second.
Then, the mobile node multicasts a neighbor solicitation message including its link layer address to the newly linked network, and starts duplicate address detection (hereinafter, to be referred to as “DAD”).
If the neighbor advertisement informing the duplicate address is not received by the mobile node within a predetermined time limit (RetransTimer), the corresponding CoA is regarded as a unique CoA, and the mobile node performs the communication using this CoA in the network. The predetermined time limit is 1000 ms according to the default.
However, if any node has already used the corresponding CoA, the node transmits to the mobile node the neighbor advertisement including its link layer address as a response for the neighbor solicitation message. As a result of this, the mobile node randomly again generates an ID for a corresponding interface, again generates a new CoA, and again performs the DAD for the generated CoA. Even after continuously performing the DAD five times, if a unique CoA can not be established, the mobile node gives up the communication in the corresponding foreign network, and waits until the link is changed.
As described above, according to the conventional mobile IPv6 protocol, even if the DAD is successful, it takes, at least, as long as a specific time limit, and if the DAD has failed, it takes several times the time limit for the hand-off. Accordingly, during this period, the mobile node is not able to use the CoA that is set as the temporal address, and therefore, is not able to perform the binding. Thus, there is generated a great deal of packet losses during the hand-off.